This invention relates to the field of high power primary batteries.
Lithium cells with inorganic nonaqueous solvents such as the oxyhalides or the thiohalides as the cathode depolarizer have been under intensive investigation over the last 15 years. The goal has been to achieve a cell with the highest energy density and best shelf life.
A well known lithium cell is the lithium/thionylchloride-carbon cell containing lithium tetrachloroaluminate as the electrolyte salt. See, for example, "Lithium Batteries," edited by John Paul Gabano, Academic Press (1983).
It was found early on that the capacity and the rate capability of the lithium/thionylchloride systems was greatly dependent on the nature of the carbon electrode. Later, it was concluded that the performance of these systems was most significantly affected by the type of carbon as much as by the techniques used to prepare the cathodes.
The most common way to produce a carbon electrode is by using an aqueous dispersion of carbon black and Teflon.RTM..* This dispersion is pressed onto a nickel screen and then dried under vacuum at elevated temperatures. While the large surface area of the carbon black electrode is an effective cathode substrate, the rate capability and the capacity of the electrode may be enhanced by using additives, e.g., copper, copper chloride, and platinum. FNT * Teflon is a registered trademark of E. I. Du Pont de Nemours
The cathode substrate serves only as an electrically conductive surface on which the solvent is reduced. During discharge, the lithium halide which forms gradually fills up the pores of the cathode substrate. If all of the substrate surface is allowed to become covered, the cathode passivates.
An alternative cathode substrate has been tried for some types of lithium cells. It has been found that semiconducting acetylene polymers, such as polyacetylene, can be doped in a controlled manner to produce a whole family of electrically conducting polymers. The doping can occur chemically or electrochemically as is well known to those skilled in the art. See, for example, Heeger et al. U.S. Pat. Nos. 4,204,216 and 4,222,903, and MacDiarmid et al. U.S. Pat. No. 4,321,114.
Thus far, polyacetylene has been used in batteries having only an organic electrolyte. Illustrative are Gray European Pat. Nos. 49 970, 50 441 and 70 107; Matsumura et al. European Pat. No. 76 119; and Japanese Pat. No. 56 52868.
It would be desirable to utilize a polyacetylene cathode substrate in place of the carbon cathode substrate in primary lithium/oxyhalide and lithium/thiohalide cells. Such a substitution is desirable since the polyacetylene has a larger active surface area for reduction of the solvent. Theoretically, higher power density should result.
Research to date, however, has indicated that polyacetylene would not be an acceptable replacement for a carbon cathode substrate in primary lithium/thionylchloride batteries. See "Compatibility of Polyacetylene with Lithium Battery Materials," Report No. GC-TR-82-288, U.S. Naval Research Laboratory Contract No. N00014-82-C-2124. In this report, it was determined that the exposure of polyacetylene to thionylchloride leads to instability of the polyacetylene. The report concluded that the favorable use of polyacetylene in conjunction with thionylchloride, without some form of protective surface coating, is unlikely.
Notwithstanding the negative results of the prior art researchers, it is an object of this invention to use polyacetylene as the cathode substrate in lithium/oxyhalide and lithium/thiohalide primary batteries.